Discontinuous or variable thickness gain modification coating for projection film and method for making same

ABSTRACT

The present invention relates to projection films and methods of making the same. In particular, the present invention relates to a projection film whereby the microspheres exhibit improved alignment on the light exit surface and have alignment on the light entrance surface that varies according to the individual microsphere diameter. In another embodiment, the present invention relates to a projection film that has the attributes of variable gain within the single projection film. In another embodiment, the present invention relates to an exposed microsphere projection film construction that provides modification of the head-on and angular pattern of light transmission (gain).

This application is a divisional of U.S. patent application Ser. No.11/074,887 filed on Mar. 7, 2005, which is hereby incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to projection films for rear projectionscreens and the like, including monitors and methods of making same, andparticularly to projection films exhibiting improved microspherealignment on the light exit surface and projection films with variablegain within a single projection film.

BACKGROUND OF THE INVENTION

Projection films are used with rear projection screens and monitors fortransmitting an image generated by a projector or the like located atthe back of the screen to the viewer on the opposite side of the screen.The viewable image is generally affected by the amount of lighttransmitted through the screen. Generally, the construction of rearprojection screens and monitors limit the amount of light transmittedthrough the screen or monitor to the viewer. It is thus desirable tohave constructions that provide increased light throughput.

Generally, rear projection screens and monitors suffer from poorangularity resulting in difficulties in viewing a projected image unlessthe viewer is facing the viewing area of such a screen or monitorhead-on. Angularity is the term used to describe the ability of a viewerto see a good image from the screen at angles other than those which arenormal to the surface of the viewable screen. For example, as the viewermoves to the side of the viewing screen, the image quality is generallydecreased. It is desirable to have projection screens and monitors whichhave improved angularity.

Projection films can be generally characterized by their performanceparameters: resolution, gain, transmission, ambient light rejection,half gain angle, and contrast. All of these parameters are generallydetermined by the structure and materials used in construction of theprojection film. The resolution of the projection film is determined, atleast in part, by the size and spacing of minute transparent particles,commonly referred to as microspheres, (e.g., the more microspherescontained on a substrate generally means increased resolution of theprojection film). The peak gain is a measure of the intensity of thelight transmitted from the rear of the film to the viewer side of thefilm as a function of angle measured from normal incidence and isnormalized with respect to a lambertian diffuser. It is determined atleast in part, by the refractive index of the microspheres and thesurrounding material. Ambient light rejection and contrast are affectedby absorption of an opaque layer, which typically is used to embed themicrospheres. The viewing angle of a particular film is defined as theangle at which the peak gain is reduced by 50%. Such angle is commonlyreferred to as the “half-gain angle”. Contrast is a measurement of thedifference in light intensity between the brightest white and thedarkest black reproducible on the viewing side of the projection film.

An exemplary prior art projection film 10 is illustrated in FIG. 1.Typically, the prior art projection film 10 includes an optically clearsupport layer 12, a light absorbing layer 14 deposited over theoptically clear support layer 12, a plurality of microspheres 16A-16Fembedded in the light absorbing layer 14, and may optionally include aconformable coating layer (or gain modification coating layer) 18deposited over the microspheres 16A-16F and/or the light absorbing layer14. In operation, light is projected from a light source (not shown) andtransmitted through the conformable coating layer 18, the microspheres16A-16F, and the optically clear support layer 12 to the viewer. Thelight absorbing layer 14 absorbs the light not transmitted through themicrospheres 16A-16F. In addition, the light absorbing layer 14 alsoabsorbs ambient light incident on the optically clear support layer 12from the viewer's side in an effort to minimize reflections to theviewer.

The conformable coating layer 18 provides a predictable light gainprofile based on the refractive index of the microspheres and therefractive index and thickness of the conformable coating layer 18. Asshown in FIG. 1, the conformable coating layer 18 is generally ofsubstantially uniform thickness across the exposed surface of themicrospheres 16A-16F. This uniform thickness modifies gain as well asimproving the focus of the light entering the film in an effort tomaximize the total light transmission through the pinhole at the lightexit surface of the microsphere 16A-16F.

As shown in FIG. 1, when the microspheres 16A-16F are relatively uniformin diameter, the microspheres 16A-16F generally penetrate through thelight absorbing layer 14 and into the optically clear support layer 12at a uniform depth. When the microspheres 16A-16F have varyingdiameters, however, as shown in FIG. 2, the conventional method ofembedding microspheres 16A-16H causes deeper penetration of the largermicrospheres (e.g., 16B, 16D, 16F) through the light absorbing layer 14and into the optically clear support layer 12. Smaller beads (e.g., 16A,16C, 16E, 16G, and 16H) can show minimal or no penetration through thelight absorbing layer 14, which essentially minimizes or eliminateslight transmission through the smaller microspheres. Another drawbackassociated with conventional processing of microspheres having varyingdiameters is that the light absorbing layer 14, which is generally madeup of a black thermoadhesive coating, may wick up the sides of thesmaller microspheres (e.g., 16A, 16C, 16E, 16G, and 16H) duringconventional processing and cause thin spots between the microspheres.These thin spots allow light to pass through the thinned interstitialcoating instead of being focused through the microspheres. This leads tothe appearance of bright spots between the microspheres.

This defect is known as “punchthrough”. Punchthrough also hasundesirable effects on the optical properties of gain and half-gainangle. Another drawback is that the thermoadhesive black coating of thelight absorbing layer 14 can be transferred to the rolls of theembedding apparatus and re-transfer portions of the thermoadhesive blackcoating to the light entrance surface of the microspheres. Thus, thereis a need to overcome the drawbacks set forth above and provideprojection films having improved microsphere alignment on the light exitsurface and projection films with variable gain within a singleprojection film.

SUMMARY OF THE INVENTION

The present invention is directed to projection films and methods ofmaking the same. In one embodiment, the present invention relates to aprojection film whereby the microspheres exhibit improved alignment onthe light exit surface and have alignment on the light entrance surfacethat varies according to the individual microsphere diameter. In anotherembodiment, the present invention relates to a projection film thatprovides for variable gain within a single projection film. In anotherembodiment, the present invention relates to a projection filmconstruction that provides modification of the head-on and angularpattern of light transmission (gain). In one embodiment, the presentinvention relates to a projection film including: a light absorbinglayer having a front surface and a back surface; and transparentmicrospheres having a plurality of diameters embedded and substantiallyuniformly aligned in the front surface of the light absorbing layer,wherein the microspheres have a front surface and a back surface thatprovide light tunnels through the light absorbing layer and protrudefrom the back surface of the light absorbing layer.

In another embodiment, the present invention relates to a method ofmanufacturing a projection film including: (a) forming a first assemblyincluding depositing a light absorbing layer having a front surface anda back surface over an optically clear support layer, wherein the frontsurface of the light absorbing layer is adhered to the optically clearsupport layer; depositing a monolayer of transparent microspheres havinga plurality of diameters over the light absorbing layer, wherein themicrospheres have a front surface and a back surface that provide lighttunnels through the light absorbing layer and protrude from the backsurface of the light absorbing layer; (b) forming a second assemblyincluding a molding layer having a front surface and a back surface; (c)laminating the back surface of the microspheres containing layer of thefirst assembly to the front surface of the molding layer of the secondassembly, whereby the molding layer proportionately conforms to thediameters of the plurality of microspheres, whereby the microspheres areembedded and substantially uniformly aligned in the light absorbinglayer; and (d) removing the molding layer whereby the microspheresexhibit improved alignment on the light exit surface and alignment onthe light entrance surface that varies according to the individualmicrosphere diameter.

In another embodiment, the present invention relates to a projectionfilm including: a light absorbing layer having a front surface and aback surface; a layer of transparent microspheres embedded in the lightabsorbing layer, wherein the microspheres have a front surface and aback surface that provide light tunnels through the light absorbinglayer and protrude from the back surface of the light absorbing layer; alayer of conformable coating of variable thickness formed over the backsurface of the microspheres.

In yet another embodiment, the present invention relates to a method ofmanufacturing a projection film including the steps of: (a) forming afirst assembly by depositing a light absorbing layer having a frontsurface and a back surface over an optically clear support layer,wherein the front surface of the light absorbing layer is adhered to theoptically clear support layer; depositing a monolayer of transparentmicrospheres over the light absorbing layer, wherein the microsphereshave a front surface and a back surface that provide light tunnelsthrough the light absorbing layer and protrude from the back surface ofthe light absorbing layer; (b) forming a second assembly including amolding layer having a front surface and a back surface wherein thefront surface of the molding layer is in contact with a conformable gainlayer having a variable thickness; (c) laminating the back surface ofthe microspheres containing layer of the first assembly to the frontsurface of the conformable gain layer of the second assembly togetherusing at least one of heat and pressure to form a projection film; and(d) removing the molding layer, whereby the projection film exhibits avariable gain.

In another embodiment, the present invention relates to a method ofmanufacturing a projection film including the steps of: (a) forming afirst assembly by depositing a light absorbing layer having a frontsurface and a back surface over an optically clear support layer,wherein the front surface of the light absorbing layer is adhered to theoptically clear support layer; depositing a monolayer of transparentmicrospheres over the light absorbing layer, wherein the microsphereshave a front surface and a back surface that provide light tunnelsthrough the light absorbing layer and protrude from the back surface ofthe light absorbing layer; (b) forming a second assembly including amolding layer having a front surface and a back surface wherein thefront surface of the molding layer is in contact with one or moreconformable coating layers at least one of the conformable coatinglayers being discontinuous; (c) laminating the back surface of themicrospheres containing layer of the first assembly to the front surfaceof the conformable gain layer of the second assembly together using atleast one of heat and pressure to form a projection film; and (d)removing the molding layer, whereby the projection film exhibits avariable gain.

In another embodiment, the present invention relates to a method ofmanufacturing a projection film including the steps of: (a) forming afirst assembly by depositing a light absorbing layer having a frontsurface and a back surface over an optically clear support layer,wherein the front surface of the light absorbing layer is adhered to theoptically clear support layer; depositing a monolayer of transparentmicrospheres over the light absorbing layer, wherein the microsphereshave a front surface and a back surface that provide light tunnelsthrough the light absorbing layer and protrude from the back surface ofthe light absorbing layer; (b) forming a second assembly including amolding layer having a front surface and a back surface wherein thefront surface of the molding layer is in contact with one or moreconformable coating layers at least one of the conformable coatinglayers having a variable thickness; (c) laminating the back surface ofthe microspheres containing layer of the first assembly to the frontsurface of the conformable gain layer of the second assembly togetherusing at least one of heat and pressure to form a projection film; and(d) removing the molding layer, whereby the projection film exhibits avariable gain.

In another embodiment, the present invention relates to a method ofmanufacturing a projection film including the steps of: (a) forming afirst assembly by depositing a light absorbing layer having a frontsurface and a back surface over an optically clear support layer,wherein the front surface of the light absorbing layer is adhered to theoptically clear support layer; (b) forming a second assembly including amolding layer having a front surface and a back surface; (c) depositinga layer of microspheres over the front surface of the molding layer ofthe second assembly; wherein the microspheres have a front surface and aback surface and the back surface of the microspheres are adhered in thefront surface of the molding layer of the second assembly; (d)laminating the front surface of the microsphere containing layer of thesecond assembly to the back surface of the light absorbing layer of thefirst assembly together using at least one of heat and pressure to forma projection film; and (e) removing the molding layer whereby themicrospheres exhibit improved alignment on the light exit surface andalignment on the light entrance surface that varies according to theindividual microsphere diameter.

In another embodiment, the present invention relates to a method ofmanufacturing a projection film including the steps of: (a) forming afirst assembly by depositing a light absorbing layer having a frontsurface and a back surface over an optically clear support layer,wherein the front surface of the light absorbing layer is adhered to theoptically clear support layer; (b) forming a second assembly including amolding layer having a front surface and a back surface wherein thefront surface of the molding layer is in contact with a conformable gainlayer having a variable thickness; (c) depositing a layer ofmicrospheres over the conformable coating layer of the second assembly;wherein the microspheres have a front surface and a back surface and theback surface of the microspheres is partially embedded in theconformable coating layer of the second assembly; (d) laminating thefront surface of the microspheres containing layer of the secondassembly to the back surface of the light absorbing layer of the firstassembly together using at least one of heat and pressure to form aprojection film; and (e) removing the molding layer, whereby theprojection film exhibits a variable gain.

In another embodiment, the present invention relates to a method ofmanufacturing a projection film including the steps of: (a) forming afirst assembly by depositing a light absorbing layer having a frontsurface and a back surface over an optically clear support layer,wherein the front surface of the light absorbing layer is adhered to theoptically clear support layer; depositing a monolayer of transparentmicrospheres over the light absorbing layer, wherein the microsphereshave a front surface and a back surface that provide light tunnelsthrough the light absorbing layer and protrude from the back surface ofthe light absorbing layer; (b) forming a second assembly including amolding layer having a front surface and a back surface wherein at leastone segment is embedded in the front surface of the molding layer and aconformable coating layer having a front surface and a back surface isdeposited on the second assembly; (c) laminating the back surface of themicrospheres containing layer of the first assembly to the front surfaceof the conformable gain layer of the second assembly together using atleast one of heat and pressure to form a projection film; and (d)removing the molding layer, whereby the projection film exhibits avariable gain.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a prior art projection film;

FIG. 2 is a cross-sectional view of a projection film havingmicrospheres of varying diameters manufactured using conventional priorart methods;

FIG. 3 is a cross-sectional view of a projection film in accordance withone aspect of the present invention;

FIGS. 4A-4D are cross-sectional views illustrating one method ofpreparing the projection film in accordance with one aspect of thepresent invention;

FIGS. 5A-5B are cross-sectional views illustrating another method ofpreparing the projection film in accordance with one aspect of thepresent invention;

FIGS. 6A-6E are cross-sectional views illustrating another method ofpreparing the projection film in accordance with one aspect of thepresent invention;

FIGS. 7A-7D are cross-sectional views illustrating another method ofpreparing the projection film in accordance with one aspect of thepresent invention;

FIGS. 8A-8B are cross-sectional views illustrating another method ofpreparing the projection film in accordance with one aspect of thepresent invention; and

FIG. 9 is a cross-sectional view illustrating another method ofpreparing the projection film in accordance with one aspect of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

As used in the specification and claims, the phrase substantiallyuniform layer refers to a layer of the construction which has athickness with little variance, such as a generally variation inthickness of less than about 5 microns, preferably a variation of lessthan about 2.5 microns, or even more preferably less than about 1.25microns. The term conformable coating layer refers to a layer thatgenerally conforms in shape to the underlying layers and/or structures,including, for example, the protruding portions of the microspheres.Here and elsewhere in the specification, drawings and claims, the rangeand ratio limits may be combined.

The invention relates to a projection film that includes an opticallyclear layer, a light absorbing layer and microspheres embedded in atleast a portion of the light absorbing layer. Optionally, themicrospheres may also be partially embedded in the conformable coating.A molding layer may be laminated to an exposed rear surface of themicrospheres using heat and pressure with the molding layer facing theexposed beads. The molding layer may surround the exposed surface of themicrospheres preventing the thermoadhesive black coating from wicking upthe sides of the microspheres. The molding layer can also push thethermoadhesive coating back down in to the interstitial areas (e.g., thearea located between microspheres), if the thermoadhesive black coatinghas already wicked up the sides of the microspheres in a previousprocessing step. When microspheres of varying diameters are used in aprojection film, the molding layer allows the larger microspheres tosink deeper into the molding layer and the smaller microspheres to sinkless deep into the molding layer, which allows for improved alignment ofthe microspheres against, and possibly into the base substrate.

The invention also relates to coating or printing a variable thicknessor discontinuous conformable coating layer (also known as a gainmodifying coating) on a molding layer to provide modification of thehead-on and angular pattern of light transmission (gain) for projectionfilm and laminating the molding layer and conformable coating layer toan exposed surface of the microspheres using heat and/or pressure. Inanother embodiment, the microspheres may also be embedded into or on themolding layer, which provides an additional advantage of aligning thetop of the microspheres so that the assembly can be subsequentlylaminated to the light absorbing layer and the optically clear supportlayer using heat and pressure. In another embodiment, the conformablecoating (or gain modifying coating) can contain microspheres ofdiffering refractive indices incorporated into the body of a continuouscoating or hanging pendent therefrom.

The present invention also relates to an exposed microsphere (or bead)construction that has a higher half gain angle than conventionalspherical systems. An increased half gain angle is accomplished byexposing the center of the transparent microspheres and having aconformable coating layer (gain modification coating) surrounding theexposed center of the microsphere (or bead).

The light absorbing layer (also referred to herein as the opaque layer)serves a number of purposes including fixing the microspheres (alsocommonly referred to as “beads”), reducing the reflectivity of theprojection film, and reducing the amount of light transmitted from theback surface through the interstices between the microspheres in thesystem to the viewer. The light absorbing layer generally has athickness sufficient for embedding the transparent microspheres. Theembedding of the transparent microspheres may be at any level providedthat the transparent microspheres form a light tunnel through the lightabsorbing layer. In one embodiment, the light absorbing layer has athickness from about 10% to 60%, or from about 10% to about 40% of thetransparent microsphere diameter. The light absorbing layer may be anymaterial that is substantially opaque and can be embedded with thetransparent microspheres to form light tunnels through the lightabsorbing layer. Likewise, the light absorbing layer may be any materialthat is malleable enough to yield when the transparent microspheres arepushed against it, such as a partially or incompletely crosslinkedurethane, a pressure sensitive adhesive, or with the addition of heat,thermoplastic polymers. The light absorbing material may also be amaterial which can form around the transparent microsphere, such as anasphalt or adhesive (e.g., a pigmented pressure sensitive adhesive).

Typically, the light absorbing layer is a combination of one or morepigments, such as carbon black, or other colorant, and one or morepolymers, including polyolefins, like polyacrylates, polyvinyl acetalssuch as polyvinyl butyral, (e.g., Butvar resins available from Solutia),polyurethanes, polyesters or polyvinylcarboxylates. The polyolefins maybe homopolymers and copolymers of C₂₋₁₂ olefins, such as ethylene,propylene, and butylene. The polyacrylates, including polymethacrylates,may be homopolymers or copolymer of C₁₋₁₂ acrylate or methacrylatemonomers, such as methyl, ethyl, propyl, butyl, hexyl, or octylacrylates or methacrylates. Here and elsewhere in the specification andclaims, the term for pendant groups is meant to include all isomericforms of the group. For instance, the use of the term octyl is intendedto cover n-octyl, isooctyl, and 2-ethylhexyl groups. Thepolyvinylcarboxylates include homo or copolymers of C₁₋₁₂ vinylcarboxylates, such as vinyl acetate, vinyl propionate and vinylbutyrate. Examples of useful commercially available polyacrylatesinclude Acrylic HI-7 from ICI and Acrylic MI-7 from Rohm & Haas. Thelight absorbing layer may contain from about 2% to about 10% by weightof the pigment and/or colorant.

Alternatively, the light absorbing layer may be a photosensitive film,in which case its optical density can be varied by exposure to actinicelectromagnetic radiation. Photochromic materials which automaticallyadjust their absorption in response to ambient light conditions also canbe used. In addition to film and polymer type materials, the lightabsorbing layer may be a wire mesh or perforated metal sheet, or acombination of wire mesh and polymers.

Transparent microspheres are embedded into the light absorbing layer.Typically the transparent microspheres are embedded to a levelsufficient to provide light tunnels through the light absorbing layer.Light tunnels are present when the microspheres are embeddedsufficiently into the light absorbing layer so that portions of themicrospheres are in contact with, and in some instances, may perforatethe front surface of the light absorbing layer, and other portions ofthe microspheres protrude through the back surface of the lightabsorbing layer. Generally, the transparent microspheres are embedded ata level of about 10% to about 80%, and in one embodiment, less thanabout 50% (preferably from about 30% to about 40%) of their diameter.

The transparent microspheres generally have a refractive index fromabout 1.4 to 2.3, or from about 1.4 to about 2.2, or from about 1.45 toabout 1.95. They are typically composed of glass, ceramic, plastic orother suitably transparent materials. The microspheres also may becomposed of photochromic materials to allow their optical properties torespond to changes in incident light intensity. Alternatively, coloredmicrospheres may be used to allow chromatic effects. Transparentmicrospheres having an average diameter of from about 25 to about 300microns are suitable for construction of the projection films describedherein. In one embodiment, the transparent microspheres have a diameterof about 30 to about 120 microns, or from about 40 to about 80 microns,or from about 50 to 65 microns. In one embodiment, the diameter of themicrospheres are determined as average diameter for a given lot ofmicrospheres. In another embodiment, the transparent microspheres aresubstantially uniform in size. In yet another embodiment, thetransparent microspheres have diameters that vary in size. In anotherembodiment, the transparent microspheres have varying refractiveindexes. In another embodiment microspheres of different diameters canbe combined in a projection film to increase the packing density.

Furthermore, in some embodiments, it may be useful to use microspheresthat are non-spherical in shape such as ellipsoids or rounded rods.These non-spherical shapes can be deposited in alignments that providedifferent optical properties in different directions. In yet anotherembodiment, the transparent microspheres are present in substantially amonolayer generally covering from 60% to about 91% of the surface areaof the back surface light absorbing layer, or from about 75% to about90%, or from about 85% to about 90% of the surface area of the backsurface of the light absorbing layer.

The microspheres can be embedded in a close-pack array (e.g., highdensity of microspheres) using a number of well known processes. In onefabrication method, a removable support material such as paper or apolymer film is coated with a thermoplastic resin binder layer which ismodified by colorant to adjust the binder layer to the desired opacity.Microspheres are then spread over the resin binder layer which issubsequently heated, allowing the microspheres to be pressed into theresin binder layer until the microspheres contact the surface of thesupport material. The microspheres may be also deposited byelectrophoresis from a fluid medium by spraying a mixture ofmicrospheres, material for the binder layer and a solvent onto a supportmaterial, or by spraying microspheres directly onto a softened resinbinder layer. The microspheres may also be deposited on a molding layer.

Another component of the projection film of the invention is that theoptically clear conformed layer. In one embodiment the conformablecoating layer is substantially uniform in thickness. In anotherembodiment, the conformable coating layer is of varying thickness toprovide the attributes of variable gain on a single projection film. Theconformable coating layer typically has a thickness of about 10% toabout 90% of the diameter of the average microsphere, or from about 20%to about 80% of the diameter of the average microsphere, or from about30% to about 70% of the diameter of the average microsphere. In oneembodiment, the conformed layer has an average thickness of from about2.5 microns to about 270 microns. In another embodiment, the thicknessis from about 7.5 microns to about 75 microns. The conformed layercomprises any polymer which has the optical clarity needed forprojection film. Typically these polymers are polyolefins, such asoptically clear polyolefins from metallocene catalysts, polyacrylates,polymethacrylates, polycarbonates, polyurethanes, polyesters, such aspolyethylene terephthates, polyvinylidene dichloride, cellophane,cellulose acetate, polyvinylidene difluorides, polyvinyl chlorides,polyvinyl acetals, and polyvinylcarboxylates. Generally, the frontsurface of the conformed layer is adhered to the back surface of thelight absorbing layer and the microspheres which protrude from the backsurface of the light absorbing layer.

The back surface of the conformable coating layer of optically clearmaterial may have a textured finish which results in reduced speckling,as discussed in U.S. Pat. No. 6,695,453, which is incorporated byreference as if fully rewritten herein. It is believed that the texturedfinish scatters reflected light with minimal effect on total lighttransmission thereby reducing speckling. In one embodiment, the texturedfinish may be a random microstructured surface such as a matte finish,or the finish may contain a pattern of three-dimensional microstructureshaving cross sections made up of very small circles, ovals, diamonds,squares, rectangles, triangles, polygons, lines, or irregular shapeswhen the cross section is taken parallel to the surface of the lightabsorbing material. The textured finish can be, in some instances, aholographic image embossed into the surface of the film.

Several procedures and techniques are known to those skilled in the artfor producing textured finishes on surfaces which can be used to formthe textured finish on the back surface of the conformed layer. Forexample, the back surface of a conformable layer of optically clearmaterial may be textured, prior to being conformed to the microspheres,by contact with a film or paper having a textured or matte finish. Thefinish on the film is replicated on the surface of the conformable layerwhen the two surfaces are joined by pressure. Alternatively the desiredsurface of the conformable layer deposited on, e.g., a release liner,can be textured by passing the construction through heated rollers, atleast one of which has a textured surface.

In another method, the image can be imparted to the back surface of theconformed layer by first printing an image or textured surface onto theface of a polymer coated surface of a casting sheet. The printing can bedone using common printing techniques such as Flexography (Flexo) andRotogravure (gravure). Heat and pressure are used to press the imageinto the face of the polymer coated casting sheet so that the top of theprint is substantially level with the polymer coated surface. Theconformable layer is then applied over the textured surface such as bylamination thereby replicating the textured or printed surface on theback surface of the conformable layer.

The microspheres that protrude from the back surface of the lightabsorbing layer have a center of curvature (e.g., the center point onthe outside surface of the microsphere furthest in distance from thelight absorbing layer), and the back surface of the conformable coatinglayer also has a center of curvature. In one embodiment the center ofcurvature of the back surface of the conformable coating layer ofoptically clear material is behind the center of curvature of themicrospheres. This alignment increases convergence of the light into themicrospheres. In another embodiment, the center of curvature of the backsurface of the conformable layer is about equal to the center ofcurvature of the microspheres thereby increasing convergences of lightinto the microspheres. In yet another embodiment, the conformable layerdoes not extend to the center of curvature of the microspheres.

The conformed layer of optically clear material provides a preliminarystage of convergence of the light into the microspheres. Also, it isbelieved that positioning the centers of curvature of the back surfaceof the conformable coating layer behind the centers of curvature of themicrospheres increases convergence of such light into the microspheres,and converges the light nearer the ideal angles for refraction of thelight through the transmission areas in front of the microspheres.

In one embodiment, the front surface of the light absorbing layer may besupported by an optically clear support layer to improve the sturdinessof the projection film. The optically clear support layer may be a glassor a polymer. The optically clear support layer generally resists thepressure exerted by the transparent microspheres during the embeddingand conforming processes. The optically clear support layer may beadhered to the light absorbing layer by an adhesive, by lamination, oras a result of coextrusion. The optically clear support layer may be anymaterial having sufficient strength to provide support to the lightabsorbing layer and having optically clear characteristics. Examples ofsupport layers include glass, polymethyl methacrylate, polyacrylics,polycarbonates, polyurethanes, such as two part polyurethanes,polyesters, such as polyethylene terephthalates, and any of thematerials described above as useful in the conformed layer of opticallyclear materials.

Another component of the projection film is a molding layer. Since theprojection films are generally manufactured through heat lamination, itis desirable that the Vicat softening point of the polymer of the lightabsorbing layer is higher than the Vicat softening point of the polymerof the molding layer. The molding layer is generally partially incontact with the microspheres and/or portions of the light absorbinglayer during preparation of the projection film. The molding layer maybe any thermoplastic polymer with the appropriate Vicat softening point.If the molding layer is composed of a polymer of similar nature to thelight absorbing layer then a layer of silicone release layer, such asthose used for pressure sensitive adhesive liners, may be used toenhance ease of separation of the layers. In one embodiment, the moldinglayer is composed of polyolefins, such as low, medium and high densitypolyethylene, propylene or mixtures thereof. The lower Vicat softeningpoint of the molding layers helps conform the molding layer to themicrospheres and the light absorbing layer. Under the pressure andtemperature of preparation, the molding layer presses the microspheresand light absorbing layer against the optically clear support layer.

The methods of making the projection films of the invention may bethrough heat lamination. In one embodiment it is desirable that asubstantially uniform conformable layer is formed on the transparentmicrospheres. In another embodiment, the conformable coating layer is ofvarying thickness to provide the attributes of variable gain on a singleprojection film. In one embodiment, it is desirable that the Vicatsoftening point of the polymer of the conformable layer is higher thanthe Vicat softening point of the polymer of the molding layer. Themolding layer is in contact with the conformable coating layer duringpreparation of the projection film. The molding layer may be anythermoplastic polymer with the appropriate Vicat softening point. If themolding layer is composed of a polymer of similar nature to theconformable layer then a layer of silicone release layer, such as thoseused for pressure sensitive adhesive liners, may be used to enhance easeof separation of the layers. In one embodiment, the molding layer iscomposed of polyolefins, such as low, medium and high densitypolyethylene, propylene or mixtures thereof. The lower Vicat softeningpoint of the molding layers helps form the conformable layer bysoftening and/or melting to conform to the surface of the transparentmicrospheres. Under the pressure and temperature of preparation, themolding layer presses the conformable layer against the transparentmicrospheres.

In one embodiment, the projection films of the invention can be preparedby the steps of: (1) providing a first assembly comprising a lightabsorbing layer having a front surface and a back surface wherein thefront surface is adhered to an optically clear support layer and amonolayer of transparent microspheres embedded in the light absorbinglayer, wherein the microspheres provide light tunnels through the lightabsorbing layer and protrude from the back surface of the lightabsorbing layer; (2) providing a second assembly comprising a moldinglayer having a front surface and a back surface wherein the frontsurface of the molding layer is in contact with the back surface of themicrospheres and/or the light absorbing layer; (3) laminating the backsurface of the microsphere containing layer of the first assembly to thefront surface of the molding layer of the second assembly, whereby themolding layer highly conforms to the microspheres and/or the lightabsorbing layer; (4) removing the molding layer whereby the microspheresexhibit improved alignment on the light exit surface and alignment onthe light entrance surface that varies according to the individualmicrosphere diameter.

In another method, the projection films can be prepared by the steps of:(1) providing a first assembly comprising a monolayer of microspheres, alight absorbing layer, and an optically clear support layer; (2)providing a second assembly comprising a molding layer having a frontsurface and a back surface wherein the front surface of the moldinglayer is in contact with a conformable gain layer having a variablethickness; (3) laminating the first and second assemblies together usingat least one of heat and pressure; (4) removing the molding layer.

In another method, the projection films of the invention can be preparedby the steps of: (1) providing a first assembly comprising monolayer ofmicrospheres, a conformable gain layer having a variable thickness; anda molding layer having a front and a back surface; (2) providing asecond assembly comprising a light absorbing layer, and an opticallyclear support layer; (3) laminating the first and second assembliestogether using at least one of heat and pressure; and (4) removing themolding layer.

In another method, the projection films of the invention can be preparedby the steps of: (1) providing a first assembly comprising a monolayerof microspheres deposited over a molding layer having a front and a backsurface; (2) applying at least one of heat and pressure to the firstassembly in order for the microspheres to slightly penetrate the moldinglayer; (3) depositing an optically clear layer over the layer ofmicrospheres so that the optically clear at least partially fills theinterstitial areas between the microspheres; (4) providing a secondassembly comprising a light absorbing layer, and an optically clearsupport layer; (5) laminating the first and second assemblies togetherusing at least one of heat and pressure; and 6) stripping the firstassembly containing the molding layer from the second assembly,containing the microspheres wherein a surface having exposed centerportion of microspheres and the areas between the microspheres have anoptically clear conformed coating.

The invention may be further understood by reference to the attachedfigures. In these figures, the top of each construction is sometimesreferred to as the “front” and the bottom is sometimes referred to asthe “back” of the construction. Accordingly the surface of each layerclosest to the top or front of the construction is referred to as the“upper surface” or the “front surface” and the surface of each layerclosest to the bottom or back of the construction is referred to as the“back surface” or the “lower surface”. In use, the light enters thefilters of the invention from the back surface, and the light is emittedfrom the front surface.

FIG. 3 is a cross-section of projection film 20 in accordance with theinvention. Projection film 20 includes an optically clear support layer22 (e.g., a polyacrylate or polyurethane), a light absorbing layer 24(e.g., polyvinylbutyral or a thermoplastic polyurethane containingcarbon black) deposited over the optically clear support layer 22,transparent microspheres 26A-26F, and a conformable coating layer 28.The transparent microspheres 26A-26F are embedded in the light absorbinglayer 24 and may contact or perforate the front surface of the opticallyclear support layer 22. Thus, the transparent microspheres 26A-26F arealigned along and/or into the substrate layer 22. The conformablecoating layer 28 is formed above the light absorbing layer 24 andgenerally between the transparent microspheres 26A-26F, leaving thecenters of the transparent microspheres 26A-26F exposed.

FIGS. 4A-4D illustrate one method for preparing the projection film 20of the invention. As shown in FIG. 4A, a first construction 20A isprovided. The construction 20A includes a monolayer of transparentmicrospheres 26A-26F deposited over a molding layer 30 and a supportlayer 32 (e.g., typically paper or a PET film). Infrared heat is used tosink the transparent microspheres 26A-26F into the molding layer 32. Thetransparent microspheres 26A-26F are top coated with a low percentsolids solution of B-90 polyvinylbutyral (PVB) to yield a dry thicknessof one-third to one-half the height of the transparent microsphere,which is identified as conformable coating layer 28, as shown in FIG.4B. A second assembly 20B is provided, as shown in FIG. 4C. The secondassembly 20B includes a light absorbing layer 24 deposited over anoptically clear support layer 22 and optionally may include a removablesupport layer 21 (e.g. typically coated paper or a PET film).

As shown in FIG. 4D, the first assembly 20A and second assembly 20B maybe laminated together using heat and/or pressure, which causes theconformable coating layer 28 to conform in the areas between the exposedfront surface of the open microspheres and the opposite surface of themicrosphere to push through the light absorbing layer 24, therebyforming light tunnels through the light absorbing layer 24. Themicrospheres 26A-26F may be pushed completely through the lightabsorbing layer 24 and partially into the optically clear support layer22. The molding layer 32 and removable support layers 21 and 32 may thenbe stripped, which yields a surface with the center portions of themicrospheres exposed and the areas between the microspheres having aconformed coating, as shown in FIG. 3.

FIG. 5 illustrates another method for preparing the projection film 20of the invention. As shown in FIG. 5A, a construction 50 includes alight absorbing layer 24 deposited over an optically clear support layer22. A conformable coating layer 28 is deposited over the light absorbinglayer 24. Microspheres 26A-26F are embedded using any conventionalembedding method. As shown in FIG. 5B, when the microspheres 26A-26F areembedded, the microspheres 26A-26F push through the conformable coatinglayer 28 and the light absorbing layer 24, thereby forming light tunnelsthrough the light absorbing layer 24. The conformable coating layer 28is displaced to the area between the microspheres 26A-26F. The removablesupport layer 21 may be removed, which yields a surface with the centerportions of the microspheres exposed and the areas between themicrospheres having a conformed coating, as shown in FIG. 3. Althoughnot shown, the conformation of the coating in the areas between themicrospheres 26A-26F may be enhanced by lamination of a suitable moldinglayer during the embedding step or in a subsequent step.

FIGS. 6A-6E represent another embodiment of the invention wherein thetransparent microspheres 26A-26H have a varying diameter. As shown inFIG. 6A, a construction 60A includes a light absorbing layer 24deposited over optically clear support layer 22. Microspheres 26A-26Hare deposited over the light absorbing layer 24 using any conventionalembedding and/or depositing method. FIG. 6B illustrates a construction60B that includes a molding layer 30 and a support layer 32. Theconstruction 60B is then laminated or exposed to heat in order for themolding layer 30 to substantially conform to the exposed surface of themicrospheres 26A-26H, as shown in FIG. 6C. The molding layer 30surrounds the exposed surface of the microspheres 26A-26H and preventsthe thermoadhesive light absorbing layer 24 from wicking up the sides ofthe microspheres 26A-26F. The molding layer 30 can also push thethermoadhesive light absorbing layer 24 back in to the interstitialareas if it has already wicked in a previous processing step. Inaddition, the molding layer 30 also allows larger microspheres (e.g.,26B, 26D, and 26F) to sink deeper into the molding layer 30 and smallermicrospheres (e.g., 26A, 26C, 26E, 26G, and 26H) to sink less deep intothe molding layer 30, thereby allowing for the improved alignment of thesurface of the microspheres that are embedded in the light absorbinglayer 24 and pushed up against and/or into the optically clear supportlayer 22, as shown in FIG. 6D. The molding layer 32 and support layers21 and 32 may then be stripped, which yields an improved projection film60 with improved alignment of the surface of the microspheres that areembedded in the light absorbing layer 24 and pushed up against and/orinto the optically clear support layer 22, as shown in FIG. 6E. Althoughnot shown, a conformable coating layer 28 may be deposited on theprojection film 60 or any of the constructions 60A and/or 60B during anystep of the process set forth above.

The following are examples of the preparation of the projection films inaccordance with certain aspects of the invention. These examples areillustrative and are not be considered limiting to the scope of theinvention. Unless otherwise indicated in the examples and elsewhere inthe specification and claims, temperatures are in degrees centigrade,parts and percentages are by weight, and pressure is at or aboveatmospheric pressure.

EXAMPLE 1

A first substrate is provided that includes a 75 micron (3 mil) layer ofpolyethylene terephthalate (SH-71 Polyester film from SKC America)laminated to a 50 micron (2 mil) layer of polymethylmethacrylate(Acrylic HI-7 from ICI). A 15 micron (0.6 mil) layer of black polyvinylbutyral (Butvar B-90 from Solutia containing 3% carbon black) isdeposited above the polymethylmethacrylate. Glass microspheres having avarying refractive index of about 1.4 to 2.0 and having an averagediameter varying from 40-70 microns are beaded on the polyvinylbutyrallayer of the first substrate. A second substrate is provided thatincludes a 150 micron paper facestock coated with a 37.5 micron lowdensity polyethylene (e.g., Felix Schoeller Technical Paper F315L). Thefirst and second constructions are pressed together (laminated) (blackpolyvinylbutyral layer with exposed microspheres of construction 1 tothe low density polyethylene layer of construction 2) at a temperatureof 285° F. (140° C.) and 100 psi using a roll laminator.

EXAMPLE 2

A first substrate is provided that includes a 150 micron (6 mil) layerof polyethylene terephthalate (SH-71 Polyester film from SKC America)laminated to a 37.5 micron (1.5 mil) layer of pigmented low densitypolyethylene is beaded with glass microspheres having a varyingrefractive index of about 1.4 to 2.0 and having an average diametervarying from 40-70 microns. A second substrate is provided that includesa 50 micron (2 mil) layer of polyethylene terephthalate (SH-71 Polyesterfilm from SKC America), a 30 micron (1.2 mil) of clear Urethane and 15micron (0.6 mil) layer of black polyvinyl butyral (Butvar B-90 fromSolutia containing 3% carbon black) is deposited above the clearUrethane. The first and second constructions are pressed together(laminated) (black polyvinylbutyral layer with clear Urethane ofconstruction 2 to the low density polyethylene layer with exposedmicrospheres of construction 2) at a temperature of 285° F. (140° C.)and 100 psi using a roll laminator.

Referring now to FIGS. 7A-7D, another embodiment of the invention isillustrated. A construction 70A includes a light absorbing layer 24deposited over an optically clear support layer 22 and optionally mayinclude a removable support layer 21 (e.g. typically coated paper or aPET film). Microspheres 26A-26F are deposited over the light absorbinglayer 24 using any conventional embedding and/or depositing method, asdiscussed above. As shown in FIG. 7B, a construction 70B includes amolding layer 30, a removable support layer 32, a uniform conformablecoating layer 28A, a discontinuous conformable coating layer 28B. Sinceincreasing the thickness of the conformable coating increases the gain,the discontinuous conformable coating layer 28B may be used to provideattributes of variable gain within a single projection film. Althoughnot shown, the conformable coating layers 28A and 28B may be combinedsingle pattern layer that has a variable thickness. The variablethickness may be achieved by using specialty coating methods or printingmethods. Common printing techniques include Flexography (flexo) andRotogravure (gravure). As shown in FIG. 7C, the constructions 70A and70B are laminated together using heating and/or pressure. Uponlamination, the conformable coating layers 28A and 28B conform to theexposed surface of the open microspheres 26A-26F. The discontinuousconformable coating layer 28B provides a increased thickness of theconformable coating layer on the projection film 70 substantiallycorresponding to portions of the conformable coating layer 28B withincreased conformable coating. Although not shown, another aspect of theinvention is to embed the microspheres 26A-26F directly with a singlelayer of discontinuous conformable coating or with multiple layers ofcontinuous and/or discontinuous conformable coating. The molding layer32 and removable support layers 21 and 32 may then be stripped.

FIGS. 8A-8B represent another method for preparing the projection film80 in accordance with the invention. As shown in FIG. 8A, construction80 includes a light absorbing layer 24 deposited over an optically clearsupport layer 22 and optionally may include a removable support layer 21(e.g. typically paper or a PET film). The construction 80B is identicalto construction 70B discussed above, except that the construction isbeaded with microspheres 26A-26F and embedded. An advantage associatedwith this embodiment is the aligning of the tops of microspheres26A-26F, so that the assembly can be subsequently laminated to the blackside of thermoplastic black on PMMA/PET using heat and pressure. Theconstructions 80A and 80B are laminated together using heating and/orpressure, the molding layer 32 and removable support layers 21 and 32may then be stripped, which yields projection film 80, as shown in FIG.8B.

FIG. 9 represents another method for preparing the projection film 90 inaccordance with the invention. As shown in FIG. 9, the conformablecoating layer 28 may contain segments 92 of differing refractive indiceseither incorporated into the body of a continuous coating or hangingpendent from conformable coating layer 28. Methods of manufacturing theprojection 90 include embedding the segments 92 in the molding layer 30using at least one of heat and pressure. The conformable coating layer28 of desired thickness is extruded or cast onto the molding layer 30containing embedded segments 92. The construction including a removablesupport layer 32, molding layer 30, segments 92 and conformable coatinglayer 28 is laminated over a construction that includes a lightabsorbing layer 24 deposited over optically clear support layer 22, anda removable support layer 21 (not shown). Other methods formanufacturing and embedding segments 92 are discussed in U.S. Pat. No.6,500,526, which is incorporated by references as if fully rewrittenherein.

While the invention has been explained in relation to its preferredembodiments, it is to be understood that various modifications thereofwill become apparent to those skilled in the art upon reading thespecification. Therefore, it is to be understood that the inventiondisclosed herein is intended to cover such modifications as fall withinthe scope of the appended claims.

1. A projection film comprising: a light absorbing layer having a frontsurface and a back surface; transparent microspheres having a pluralityof diameters embedded and substantially uniformly aligned in the frontsurface of the light absorbing layer, wherein the microspheres have afront surface and a back surface that provide light tunnels through thelight absorbing layer and protrude from the back surface of the lightabsorbing layer.
 2. The projection film of claim 1, wherein themicrospheres have a have plurality of diameters in the range of about 25to 300 microns.
 3. The projection film of claim 1, wherein the frontsurface of the light absorbing layer is adhered to an optically clearsupport layer.
 4. The projection film of claim 3, wherein themicrospheres perforate the light absorbing layer and are substantiallyuniformly aligned in the optically clear support layer.
 5. Theprojection film of claim 3, wherein the optically clear support layerincludes a polyester, a polyurethane, or a polymethacrylate.
 6. Theprojection film of claim 1, wherein a conformable coating layer isdeposited over the back surface of the light absorbing layer andmicrospheres.
 7. The projection film of claim 6, wherein the conformablecoating layer has an average thickness of from about 2.5 microns toabout 270 microns.
 8. The projection film of claim 1, wherein themicrospheres have a refractive index ranging from about 1.4 to about2.3.
 9. A method of manufacturing a projection film comprising: (a)forming a first assembly including depositing a light absorbing layerhaving a front surface and a back surface over an optically clearsupport layer, wherein the front surface of the light absorbing layer isadhered to the optically clear support layer; depositing a monolayer oftransparent microspheres having a plurality of diameters over the lightabsorbing layer, wherein the microspheres have a front surface and aback surface that provide light tunnels through the light absorbinglayer and protrude from the back surface of the light absorbing layer;(b) forming a second assembly including a molding layer having a frontsurface and a back surface; (c) laminating the back surface of themicrospheres containing layer of the first assembly to the front surfaceof the molding layer of the second assembly, whereby the molding layerproportionately conforms to the diameters of the plurality ofmicrospheres, whereby the microspheres are embedded and substantiallyuniformly aligned in the light absorbing layer; and (d) removing themolding layer whereby the microspheres exhibit improved alignment on thelight exit surface and alignment on the light entrance surface thatvaries according to the individual microsphere diameter.
 10. The methodof manufacturing a projection film according to claim 9, wherein thelayer of microspheres deposited have a diameter of from about 25 to 300microns.
 11. The method of manufacturing a projection film according toclaim 9 further comprising adhering an optically clear support layerabove the light absorbing layer after the step of removing the moldinglayer.
 12. The method of manufacturing a projection film according toclaim 11, wherein the layer of microspheres perforates the lightabsorbing layer and are substantially uniformly aligned in the opticallyclear support layer.
 13. The projection film of claim 11, wherein theoptically clear support layer includes a polyester, a polyurethane, or apolymethacrylate.
 14. The method of manufacturing a projection filmaccording to claim 9, wherein, the step of laminating involves applyingat least one of heat and pressure to at least one of the first andsecond assemblies.
 15. A method of manufacturing a projection filmcomprising the steps of: (a) forming a first assembly by depositing alight absorbing layer having a front surface and a back surface over anoptically clear support layer, wherein the front surface of the lightabsorbing layer is adhered to the optically clear support layer; (b)forming a second assembly including a molding layer having a frontsurface and a back surface wherein the front surface of the moldinglayer is in contact with a conformable gain layer having a variablethickness; (c) depositing a layer of microspheres over the conformablecoating layer of the second assembly; wherein the microspheres have afront surface and a back surface and the back surface of themicrospheres is partially embedded in the conformable coating layer ofthe second assembly; (d) laminating the front back surface of themicrospheres containing layer of the second assembly to the back surfaceof the light absorbing layer of the first assembly together using atleast one of heat and pressure to form a projection film; and (e)removing the molding layer, whereby the projection film exhibits avariable gain.
 16. The method of manufacturing a projection filmaccording to claim 15, wherein the step of forming the variablethickness conformable coating is provided by printing one or more layerson the conformable coating layer.
 17. A method of manufacturing aprojection film comprising the steps of: (a) forming a first assembly bydepositing a light absorbing layer having a front surface and a backsurface over an optically clear support layer, wherein the front surfaceof the light absorbing layer is adhered to the optically clear supportlayer; depositing a monolayer of transparent microspheres over the lightabsorbing layer, wherein the microspheres have a front surface and aback surface that provide light tunnels through the light absorbinglayer and protrude from the back surface of the light absorbing layer;(b) forming a second assembly including a molding layer having a frontsurface and a back surface wherein at least one segment is embedded inthe front surface of the molding layer and a conformable coating layerhaving a front surface and a back surface is deposited on the secondassembly; (c) laminating the back surface of the microspheres containinglayer of the first assembly to the front surface of the conformable gainlayer of the second assembly together using at least one of heat andpressure to form a projection film; and (d) removing the molding layer,whereby the projection film exhibits a variable gain.
 18. The method ofmanufacturing a projection film according to claim 17, wherein theembedded at least one segment has a refractive index substantially equalto a refractive index associated with the deposited conformable coatinglayer.
 19. The method of manufacturing a projection film according toclaim 17, wherein the embedded at least one segment has a refractiveindex different than a refractive index associated with the depositedconformable coating layer.
 20. The method of manufacturing a projectionfilm according to claim 17, wherein the segments are embedded to belaminated over the back surface of the microspheres.
 21. A projectionfilm comprising: a light absorbing layer having a front surface and aback surface; a layer of transparent microspheres embedded in the lightabsorbing layer, wherein the microspheres have a front surface and aback surface that provide light tunnels through the light absorbinglayer and protrude from the back surface of the light absorbing layer;and wherein the front surface of the microsphere has an exposed centerportion and the areas between the microspheres have an optically clearconformed coating.
 22. A method of manufacturing a projection filmcomprising the steps of: (a) forming a first assembly comprising amonolayer of microspheres deposited over a molding layer having a frontand a back surface and applying at least one of heat and pressure to thefirst assembly in order for the microspheres to slightly penetrate themolding layer (b) depositing an optically clear layer over the layer ofmicrospheres so that the optically clear layer at least partially fillsthe interstitial areas between the microspheres (c) forming a secondassembly by depositing a light absorbing layer having a front surfaceand a back surface over an optically clear support layer, wherein thefront surface of the light absorbing layer is adhered to the opticallyclear support layer; (d) laminating the first and second assembliestogether using at least one of heat and pressure; (e) removing themolding layer from the second assembly containing the microsphereswherein the microsphere surface has an exposed center portion and theareas between the microspheres have an optically clear conformedcoating.